Metallo-organic precursors have been used in recent years to prepare advanced materials such as titanium nitride, vanadium nitride, silicon carbide, silicon nitride, etc. These advanced materials advantageously have been deposited onto transparent glazings, e.g., glass, and other substrates by well-known coating processes such as, for example, atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), laser induced chemical vapor deposition (LCVD), and the like. Glazings having these advanced materials coated thereon are particularly useful in automotive and architectural applications which require reduced solar and infrared radiation transmittances.
Titanium nitride is a particularly useful advanced material having several desirable properties such as, for example, high melting point (2,950.degree. C.), high hardness (8-9 on the Moh scale), excellent strength, high electrical conductivity, excellent solar and infrared reflectances, and nonreactivity with a variety of corrosive atmospheres. Furthermore, it is substantially unaffected by acids, excepting aqua regia; however, alkali compounds may cause its decomposition.
Conventional methods for preparing titanium nitride include the high temperature reaction of a source of titanium such as, for example, titanium tetrachloride with a source of nitrogen such as, for example, ammonia. Such a method is disclosed in U.S. Pat. No. 4,535,000 to Gordon. This chemical vapor deposition process has been used to form a film of titanium nitride on a ribbon of glass as it is being produced by the well-known float glass process.
It is known to prepare titanium nitride by the Pyrolysis of a polymeric precursor formed by reacting ammonia with a titanium dialkylamide. See Brown, G. M. and Maya, L., "Ammonolysis Products of the Dialkylamides of Titanium, Zirconium, and Niobium as Precursors to Metal Nitrides," Journal of the American Ceramic Society, v. 71 (1988) 78-82. Specifically, a titanium dialkylamide such as, for example, tetrakis(dimethylamido)titanium is reacted with liquid anhydrous ammonia to form an imido- or nitride-bridged polymeric precursor having the general formula Ti.sub.3 (NX.sub.2)(NH.sub.2).sub.2 N.sub.3, wherein X is an alkyl group. Thereafter, the precursor is pyrolyzed in an ammonia atmosphere to prepare titanium nitride. During the initial stages of the pyrolysis process, NHX.sub.2 and NH.sub.3 are released, forming a compound having the approximate composition Ti.sub.3 N.sub.4. At a temperature of approximately 700.degree. C. to 800.degree. C., additional nitrogen is released thereby forming partially crystalline titanium nitride.
Also, it is known to prepare titanium nitride by the pyrolysis of a polymeric precursor formed by reacting tetrakis(dimethylamido)titanium with either liquid ammonia or a primary amine. See Seyferth, D. and Miganani, G., "The Preparation of Titanium Nitride and Titanium Carbonitride by the Preceramic Polymer Route," Gov. Rep. Announce. Index (US), v. 88 (1988) 827, 109. The publication discloses that tetrakis(dimethylamido)titanium is reacted with a primary amine such as n-butylamine to form a polymeric precursor which pyrolyzes under a stream of ammonia to give fairly Pure titanium nitride. Pyrolysis is carried out at a temperature of approximately 1,000.degree. C.
Cowdell, R.T. and Fowles, G.W., "Amine Compounds of the Transition Metals. Part VI. The Reaction of Titanium (IV) Cloride with Some Aliphatic Amines," Journal of the Chemical Society (1960) 2522-2566, discloses a reaction between titanium tetrachloride and several primary amines. The article discloses that aminobasic titanium chlorides TiCl.sub.2 (NHR).sub.2 and their corresponding alkyl amine complexes TiCl.sub.2 (NHR).sub.2,2NHR are formed. The article, however, does not suggest that such compounds may be utilized to form titanium nitride.
Finally, a recently allowed U.S. Pat. application, Ser. No. 07/625,180, discloses that a titanium tetrahalide may be reacted with at least one disilazane to prepare a titanium-containing metallo-organic precursor, which thereafter may be pyrolized to form bulk titanium nitride.
It would be desirable to prepare organometallic percursors to titanium nitride, which could be used as single-source precursors in a chemical vapor deposition process for forming a coating of titanium nitride on a substrate, or in a pyrolysis process to prepare bulk titanium nitride.
It must be noted that the prior art referred to hereinabove has been collected and examined only in light of the present invention as a guide. It is not to be inferred that such diverse art would otherwise be assembled absent the motivation provided by the present invention, nor that the cited prior art when considered in combination suggests the present invention absent the teachings herein.